pregnant women getting ultrasound
Louise Broadbridge
Louise Broadbridge

The 20 week scan – what to expect

Pregnant women are offered a routine ultrasound examination at 20 weeks of pregnancy, which is known as the anomaly scan.

For most expectant mums, this will be the second ultrasound scan they have following on from the 12-week dating scan. However, if your pregnancy is high risk, there have been complications or you have chosen to pay for private scans, you may have been given additional ultrasound examinations.

What is the purpose of the 20-week scan?

For many parents-to-be, the 20-week scan is seen as an opportunity to get a detailed look at their baby and potentially find out whether they are a boy or a girl. While many sonographers will happily tell parents the sex of their baby if they can see it during the scan and they want to find out, this is not the purpose of this scan.

The scan is a detailed medical examination, which checks how your baby is developing and screens for a number of health issues. During the scan, the sonographer will check your baby’s bones, heart, spinal cord, kidneys, face and abdomen.

In addition to checking on the baby’s general development, the sonographer will specifically look for signs of 11 rare conditions. These are anencephaly, open spina bifida, cleft lip, gastoschisis, diaphragmatic hernia, serious cardiac abnormalities, lethal skeletal dysplasia, Edwards’ syndrome (also known as T18), Patau’s syndrome (also known as T13), exomphalos and bilateral renal agenesis.

The scan will also allow the sonographer to check the position of the placenta. If you are found to have a low-lying placenta at 20 weeks, you will need to have another ultrasound scan at 32 weeks to see whether it has moved.

Will the 20-week scan spot if my baby has a medical issue?

Not all medical issues can be spotted during the anomaly scan so there is still a chance your baby may have a disability or health problem even if the 20-week scan did not raise any concerns. There is also a small chance your baby may have one of the conditions the sonographer was looking for as some are more challenging to identify than others.

However, for the majority of women, the scan will find their baby is developing as normal and the appointment will be a precious opportunity to get a glimpse of their child in the womb.

If the scan does identify a potential issue, you may be referred for further tests. You will given information about what has been found and what it might mean and your consultant or midwife will talk through what your options are. In some cases, you may be referred to a specialist and further monitoring may be required.

When is the anomaly scan carried out?

Although the anomaly scan is often called the 20-week scan, it may not always be carried out at exactly 20 weeks. Your ultrasound appointment will usually be carried out between 18 weeks and 21 weeks of pregnancy, which is around the halfway point.

What can I expect to happen during my 20-week scan?

Like the 12-week scan, it will usually take place at a hospital, although there are some other medical centres with ultrasound facilities. The scan itself will be carried out in a dimly-lit room by a sonographer who will be able to view 2D black and white images of your baby.

You may be asked to make sure you have a full bladder before the scan so drink plenty of water. Take care not to overdo it though as the scan will be more uncomfortable if you are bursting for the toilet right from the start.

You will be asked to lie back on a couch and the sonographer will squirt some gel onto your bump. You will be asked to arrange your clothes so your bump is exposed so it is a good idea to wear a top and trousers or a skirt rather than a dress to make this easier. The sonographer will usually tuck some paper towels around your clothes to protect them from the gel.

The sonographer will move a handheld probe over your bump to get good images of your baby and the different parts of their body. At times, they might have to apply some pressure and this can feel a little uncomfortable but it should not hurt.

It is really important that the sonographer has a clear view of their screen during the scan. They have a lot of measurements to take so there may be times when you cannot see the screen and they may be quiet.

Please don’t worry if your sonographer doesn’t talk much while performing the scan. This is usually just because they are focusing on the task in hand rather than an indication of a problem.

The scan itself will usually take around half an hour, although it may be longer if your baby is in an awkward position. You may even be asked to move around a little to try and get your little one to change positions so the sonographer can get a clearer view.

Can I find out my baby’s gender during this scan?

Checking your baby’s sex is not the purpose of the 20-week scan but most sonographers will offer to tell parents if they want to know. Your baby’s sex organs may not always be clearly visible during an ultrasound scan and your sonographer may tell you that they are not sure of the gender.

Even if they are able to tell you whether your baby is a boy or a girl, they cannot guarantee that this is completely accurate. There is always a small margin of error so don’t rush out and spend huge amounts of money on blue or pink clothing.

Some hospitals may refuse to discuss your baby’s sex during the 20-week scan as part of their policy. Speak to your midwife if you are unsure of the policy in your area.

Will I be able to get a photograph?

Most hospitals will offer the option of getting an ultrasound photograph but check what the policy is in your particular area. Any photographs will not be taken until the end of the scan when all the medical checks and measurements have been taken.

You may be asked to pay a fee for the images and the cost varies depending on the individual hospital.

Will I be able to bring someone with me to the scan?

You will be able to bring a partner, friend or loved one to your 20-week scan with you. The hospital may limit you to just one person and most places do not allow children but check with your midwife to see what the policy is in your area.

If you don’t have a partner or they are unable to attend the appointment, it is still a good idea to ask someone to accompany you for support. There is a possibility that you might find out there is a potential problem with your pregnancy so having someone with you can make the experience less stressful.

Is the 20-week scan compulsory?

All medical checks and screening are optional and some parents may choose not to find out whether their baby might have a medical condition or disability. The scan itself is safe and there are no known risks to either yourself or your baby.

If the scan does identify an issue, the medical team may recommend further tests but it is completely up to you whether you choose to have these tests.

If you are unsure about whether you want to have the 20-week scan, you can discuss your concerns with your midwife. She will not pressure you into having the scan and if you choose not to have it, the rest of your antenatal care will still continue as normal.

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